Modelling blast-induced liquefaction of tailings backfill at early ages

Mamadou Fall

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: ENERGY RESOURCES - I Mining and Tailings

ABSTRACT: Although the production blasting remains a routine in contemporary mine operations, the knowledge on the response oftailings backfills subjected to such dynamic loading isinsufficient. Particularly, the understanding of the liquefaction offresh tailings backfills caused by blast is even more limited, despite that those materials have long been acknowledgedas liquefiable porous media.Amodified viscoplastic cap model has been developed in this study to capture theliquefactionof freshtailings backfillscaused by blasting. This model can account for the effect of high-rate impacts by theincorporation of viscosity, capture the nonlinearity in volumetric deformation under high pressure with an equation ofstate, and also simulate the volumetric hysteresiswhich causesblast-induced liquefactionwith a cap model. Theproposed model is validated against a field explosion test on saturated tailings deposit. The simulated results indicategood agreement with the experimental data.Moreover, thesimulated time histories of the irrecoverable volumetric straincan represent well the build-up of residual excess pore water pressure, and are consistent with the mechanism of blast-induced liquefaction.R•SUM•Bien que la production pardynamitage resteune routine dansles op†rations mini‡rescontemporaines, lacompr†hension du comportement des remblais miniers soumis …des sollicitations dynamiques est insuffisante. Enparticulier, la compr†hension de la liqu†faction des remblais de r†sidus frais caus†s par l'explosion est encore pluslimit†e, malgr† que ces mat†riaux aient longtemps †t† reconnuscommedesmilieux poreux liqu†fiables. Un mod‡levisco-plastiquea †t† d†velopp† dans cette †tude pour capturer la liqu†faction des remblais de r†sidusminiersfraisprovoqu†s par le dynamitage. Ce mod‡le peut tenir compte de l'effetde haute vitesse d—impactspar l'incorporation de laviscosit†,dela non-lin†arit† dans la d†formation volum†trique sous haute pression avec une †quation d'†tat,et†galement simuler l'hyst†r†sis volum†trique qui provoque la liqu†faction induite par explosion. Le mod‡le propos†estvalid† avec un test d'explosionsurund†p–t de r†sidusminierssatur†s.Les r†sultats simul†s indiquentunebonneconcordance avec les donn†es exp†rimentales. Par ailleurs, les†coulements ded†formation volum†trique irr†cup†rablesimul†speuvent repr†senter bien l'accumulation de pression de l'eau r†siduelle de surpressions interstitielles et sontenaccordanceavec le m†canisme de liqu†faction induite par l'explosion.1INTRODUCTIONUnderstanding and predicting the liquefactionsusceptibility of soils under blast loading is a veryimportant topic in civil, mining, defensive and protectionengineering.Liquefactioncan not only occur in naturalgranular soils (sand, silt), but also in mining geotechnicalstructures constructed of man-made granular soils (ortailings), such as tailings impoundments, fresh cementedand uncemented tailings backfill (paste andhydraulicbackfill (PB and HB))(Fragaszyand Voss1986, Bolton etal.1994,Ashford et al.2004,Le Roux, 2004,Al-Qasimi etal.2005,Charlie et al.2013). However, previous researchwork on the liquefaction susceptibility of man-made soilsor geotechnical miningstructures have mainly focusedonly on liquefaction caused by seismic loading (Le Roux2004,Saebimoghaddam 2010,Shahsavari et al. 2014,Ferdosi et al. 2015), and thus liquefaction caused byblasting has yet to be thoroughly examined. In fact, it isvitalfor this research work to be carried out now, sinceblast production is routinely used in contemporary mineoperations.The conventional practices ofcharacterizing blast-induced liquefactionhave been the development ofempirical relationships over decades. They are subjectedto substantial amount of time and financial costs as wellas safety concerns, and the test results are site-specificand problematic when applied to different cases.To date,avariety of constitutive models for simulating soil behaviorunder blast loading are available, and they excel with theirbenefits of overcoming previous issues associated withphysical testing, but extremely rare studies have focusedon the mathematical modelling of blast-inducedliquefaction.Characterizing blast-induced liquefaction is differentfrommodellingthatofearthquakes in that the effectivestress principle is adopted for the latter, while suchaconcept is no longer valid forblastloadingand the fluidphase entrapped will simultaneously deform with the soilskeleton. This is because interstitial fluids with evenhigher stiffness are not able to drain during theinstantaneous loading condition.(Wang et al. 2004,Grujicic et al. 2008,Wang et al. 2008,An et al. 2011).Furthermore, with transient blast loading, the high strain-rate effect should be considered as a very crucial factoron the stiffness and strength of the material (Bolton et al.1994). Consequently, according to Grujicic et al. (2008), acomplete formulation to solve such transient nonlinear

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